Overhead projectors have long been used by educators and lecturers to project an illuminated and enlarged image on a screen for viewing by an audience. With the increasing use of computers, powerful calculators and other electronic computing devices as pedagogical, demonstration or illustration devices, there is a need to enlarge and project the computer and/or calculator screen display for group viewing.
One attempt to achieve this capability employs a duplicate liquid crystal display (LCD) coupled to the calculator to generate the same data and configuration as displayed on the calculator display screen. This duplicate liquid crystal display is then positioned approximately ten inches above the projector document surface by the use of a stand or platform. Such a stand usually incorporates a magnifying lens positioned above the duplicate liquid crystal display to further enlarge the projected image in order to project an adequately large image.
Although such setups achieve the desired function, i.e., enlarge and project the calculator screen display, they have fatal flaws. Due to the internal projector condenser lens arrangement, the light emitting from the projector light source is more concentrated at the elevated point than at the document surface. The elevated duplicate liquid crystal display is thus subject to more concentrated energy per square inch, which translates to its substantial heating. Since typical liquid crystal displays have an operating temperature upper limit of 50.degree. to 80.degree. C., the elevated stand arrangement quickly causes overheating of the duplicate liquid crystal display and its associated electronics. As a result, the projected image darkens and yields progressively less contrast between the pixels on the display and the lit background. Frequent contrast adjustment or shutting off the projector therefore becomes necessary within the time span of a typical class session or lecture.
One solution to the duplicate liquid crystal display overheating and darkening problem is to use a pre-shaped heat shield placed on the projector document surface beneath the stand to decrease the amount of light energy striking the duplicate liquid crystal assembly. Because the heat shield is usually a separate piece of cardboard with no obviously discernable function, it is easily overlooked, lost or discarded by the unsuspecting user. The heat shield, although reducing the amount of heating in the liquid crystal display, is still unable to prevent overheating for a prolonged period of use. This solution is therefore unsatisfactory and merely acts as a bandage to the underlying problem.
Another solution to the duplicate liquid crystal display overheating and darkening problem is to use forced-air convection. A motorized fan is incorporated into the duplicate liquid crystal display assembly to vent air upward from the bottom surface of the duplicate liquid crystal display. However, the added fan and associated hardware not only draw additional electricity from the power source, but also they contribute added weight and bulk to the duplicate liquid crystal display assembly. Since portability is a requisite specification in the design of the calculator or computer screen projector, this solution is also undesirable.
Accordingly, a need has arisen for a remote calculator or computer screen projection display that overcomes the above-described disadvantages and problems.